Ask what must survive the current exchange
A direct prompt usually fits when the work is disposable, low consequence, and easy to inspect immediately. Examples include generating title directions or rephrasing a paragraph that the user already understands.
A specification fits when the task has approved sources, several transitions, a separate review, correction behavior, or an output that must survive interruption. It becomes more important when the work can affect data, money, external communication, or reputation.
Compare both choices on one synthetic job
The request “make a brief from these workshop notes” can work as a prompt when a person will inspect everything in the same sitting.
The full journey needs a specification because the note confirms an audience, two-hour offer, and evidence constraint while leaving schedule and price unknown. The first brief adds a Saturday sentence. Review removes it, and the checkpoint preserves the reason.
That sequence needs declared inputs, outputs, stopping conditions, and review criteria. A long prompt may describe the process, but it does not create a durable state model for resumption and inspection.
Use consequence as the tie-breaker
Choose the fuller definition when a wrong assumption can change an account, send a message, alter a durable file, or mislead another person. Also choose it when a second person must understand why the result changed.
Choose the lighter prompt when the work stays exploratory and the accountable person can judge it at once. Do not add ceremony where a short question and direct inspection are enough.
The fabricated brief demonstrates the decision rule. It cannot prove that one format improves every task or model.